Typical internal combustion engines operate by introducing fuel and air into cylinders for combustion. The pistons move within the cylinders to compress the fuel and air mixture, which combusts. The burning fuel expands the air volume in the cylinder producing power. A sliding seal between each piston and the respective bore in which the piston is operating helps seal the compressing fuel and air mixture, and also seals combustion products in the cylinder as the volume expands and pressure in the cylinder increases. Exhaust products, however, may leak past the piston seals and enter an interior volume of the crankcase. Exhaust products may also enter internal engine cavities though intake or exhaust valve seals, turbocharger cooling oil streams and, possibly, other sources. These combustion products are sometimes referred to as “blow-by gases” or “blow-by.” Blow-by gases contain contaminants normally found in exhaust gases such as hydrocarbons (HC), carbon monoxide (CO), NOx, soot, and unburned or partially burned fuel. Lubricating oil in the crankcase tends to be atomized or otherwise entrained in the hot blow-by gases to form what may be termed an aerosol.
Blow-by gases in the crankcase, including entrained lubricating oil, are typically filtered or otherwise treated to remove oil before being provided back to the air intake system of the engine, or to the environment. Other systems direct the crankcase emissions into the engine exhaust system where they receive emission treatment to the same extent engine exhaust gases receive treatment before release to the environment. Those systems where the crankcase emissions are reintroduced into the engine for burning belong to the class of closed crankcase ventilation (CCV) systems, while systems in which crankcase emissions are processed and released to the environment are generally referred to as open crankcase ventilation (OCV) systems.
Some engines, such as large diesel engines, for example, utilize forced induction to enhance the power output of the engine. This may involve superchargers or turbochargers. Returning crankcase emissions to the intake side of a compressor in a supercharger or turbocharger can result in fouling of the compressor wheel in a relatively short time period. The fouling is compounded in multiple turbocharger systems as the heat increases in downstream compressor units. Additionally, cooling units downstream of a supercharger or turbocharger may be fouled. Therefore, crankcase emissions are typically purified before being returned to the intake in a supercharged or turbocharged engine.
A crankcase ventilation system is disclosed in U.S. Patent Application Pub. No. 2014/0290634A1 to Slaughter et al. (“Slaughter”). Slaughter describes A crankcase ventilation system for an internal combustion engine having a cylinder block that at least partially defines at least one cylinder, and includes a valve cover configured to be mounted on an individual cylinder head corresponding to an individual cylinder and form a cavity therein. A crankcase ventilation opening is associated with the valve cover, and a crankcase breather is incorporated into the valve cover.